Minimal c interface

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/404

• Minimal C Interface
• Configuration via json files
• Renaming of many classes and functions (In order to comply with best-practices as formulated by https://google.github.io/styleguide/cppguide.html)

Integration tests are in caosdb-cppinttest!1 (merged)

Focus

• Please take a look at the c-interface functions:
  • I the naming consistent?
  • I see one problem regarding the destructors: When a client uses caosdb_connection_connection_manager_get_default_connection to get the default connection, the destructor caosdb_connection_delete_connection should not be called, because the connection object is actually owned by the ConnectionManager. Maybe, we should prevent the deletion of the wrapped connection somehow, when the connection is owned by the ConnectionManager?
• ConfigurationManager and ConnectionManager:
  • These two singletons are tightly coupled. When the ConfigurationManager is being reset, also the ConnectionManager resets. Is this a good behavior?
• There is currently no error/exception handling in the c-interface. I will add this in https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/390

Test Environment

Please try and setup a client (e.g. the ccaosdbcli) with a json configuration file.

Check List for the Author

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• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

For further good practices have a look at our review guidelines.

README_SETUP.md

@@ -9,6 +9,26 @@ We use [cmake](https://cmake.org) as build tool.
 3. `cmake -B . ..`
 4. `cmake --build .`
 
+You may also want to install libcaosdb system-wide to
+`CMAKE_INSTALL_PREFIX/lib` by
+
+5. `cmake --install .`
+
+The default install prefix is `~/.local`. It can be set by adding
+`-DCMAKE_INSTALL_PREFIX=/path/to/install/prefix` to the first cmake
+command (3.).
+
+### How to build on MacOS
+
+Instead of the above conan command (2.) use
+
+2. `conan install .. -s "cppstd=11"`
+
+and continue as you would when building on a Linux system. You may
+have to add `build/lib/` (or, alternatively after installation,
+`CMAKE_INSTALL_PREFIX/lib`) to your `DYLD_LIBRARY_PATH` environmental
+variable.
+
 ## Unit Tests
 
 ### Build
@@ -52,6 +72,26 @@ The coverage report can be viewed in a browser by opening
 
 Please adhere to [Google's C++ naming conventions](https://google.github.io/styleguide/cppguide.html#Naming).
 
+## Client Configuration
+
+You can use a json file for the configuration of the client. See
+`test/test_data/test_caosdb_client.json` for an example. You may use
+`caosdb-client-configuration-schema.json` to validate your schema.
+
+The client will load the configuration file from the first existing
+file in the following locations (precedence from highest to lowest):
+
+1. A file specified by the environment variable
+   `$CAOSDB_CLIENT_CONFIGURATION`.
+2. `$PWD/caosdb_client.json`
+3. `$PWD/caosdb-client.json`
+4. `$PWD/.caosdb_client.json`
+5. `$PWD/.caosdb-client.json`
+6. `$HOME/caosdb_client.json`
+7. `$HOME/caosdb-client.json`
+8. `$HOME/.caosdb_client.json`
+9. `$HOME/.caosdb-client.json`
+
 ## Documentation
 
 In the build directory, run